The present invention relates to a device to control the aiming and focusing of laser systems on a target. It can be applied especially in the field of power lasers used for example to study the physics of thermonuclear plasmas. Plasmas of this kind are obtained by focusing laser beams on the periphery of a target positioned for example within a capsule located in a cavity in which a high vacuum is present.
Several beams have to be focused on a target to obtain the energy to trigger a nuclear fusion reaction. The number of beams may for example exceed 200. A beam coming from a medium powered driving laser, generally a neodymium/glass laser with a wavelength equal to 1.054 .mu.m giving energy of the order of 1 joule, is amplified by means of optical amplifiers placed in a multiple-passage amplification system. This beam is then transmitted to non-linear crystals used to obtain an ultraviolet output beam with a wavelength equal to 0.351 .mu.m whose energy may go up to several kilojoules. The entire set of beams may then provide the target with energy equivalent to several hundreds of kilojoules.
There may be two types of targets. A first type of target consisting of a microbead with a diameter of 1 mm is engaged directly. A second type of target is engaged indirectly. In this case the preceding microbead is located within a cylinder with a diameter for example of 1 cm. In the former case, it is necessary to focus the beams on a precise point of the bead, at the center, on the surface or elsewhere. In the latter case, the beams must be focused on the circular apertures made in the bases of the cylinder. In both cases, the beams must therefore converge at a precise point. This requirement means that it is necessary to ensure transversal settings in the x, y directions and longitudinal setting in the z direction.
The aiming and focusing of the beams on the target must be done with 3D precision, for example of the order of 50 .mu.m, it being possible for the target to be positioned, depending on the firing operation, in a spherical domain with a radius of 5 mm.
The aim of the invention is to enable a precise setting of the aiming and focusing of the laser system on a target of the first or second type.